THE EFFECT OF REFLEX EXCITATION AND INHIBITION ON THE RESPONSE OF A MUSCLE TO STIMULATION THROUGH ITS MOTOR NERVE

Abstract

If reflex activity were mediated by impulses different in kind from those evoked by the electrical stimulus, or if decerebrate tonus involved a different mechanism or a different kind of function from other reflex contraction, these activities would presumably not render the motor nerve fibers refractory to artificial stimuli. The mechanical and electrical responses of an extensor muscle in the decerebrate cat, evoked by single stimuli applied to its motor nerve, were compared with one another during various forms of reflex activity of the extensor muscle; namely, decerebrate tonus, post-inhibitory rebound, the crossed extension reflex, and in reflex inhibition of the extensor center. The response to the motor-nerve stimulus is larger during inhibition than during reflex excitation, and the greater the reflex excitation the less the response to the motor-nerve stimulus. Apparently during reflex activity a certain percentage of the motor nerve fibers, or the muscle fibers they innervate, are rendered refractory to stimuli applied directly to the motor nerve. This points to an essential resemblance between the reflex impulses and those artificially produced. Even a vigorous reflex usually causes but a small decrease in the response to a motor-nerve stimulus; this attests the small proportion of fibers in a muscle which take part in its reflex contraction. This method revealed no apparent qualitative difference between tonus and the extensor reflexes.